Aladdin's Window

To finish Aladdin's Window—i.e. to attempt to complete
something begun by a great genius, but left imperfect. The genius of
the lamp built a palace with twenty-four windows, all but one being
set in frames of precious stones; the last was left for the sultan to
finish; but after exhausting his treasures, the sultan was obliged to
abandon the task as hopeless.

Tait's second part of Dryden's Absalom and Achitophel is an
Aladdin's Window.